THE INCISORS. 611 



render it impossible for the teeth to fulfil their functions, and would determine 

 their early shedding, were it not for this fortunate restoration, in advanced age, 

 to preserve their properties for a still long time. 1 



If, as Simonds 2 thinks, this radical cement be the consequence of the trans- 

 formation of the ivory into bone, the teeth upon which it is deposited should 

 not augment in volume in consequence of its appearance ; in the centre of the 

 dental table is always found, in such cases, an area of dentine the dimensions 

 of which are exactly the same as those of the normal root. The peripheral 

 cement is therefore superadded to the tooth, and is not formed at the expense 

 of the latter. 



2d. The enamel, E, is the true protective layer of .the teeth. Situated 

 underneath the cement, it represents a sort of polished coating covering the 

 whole of the surface of the dentine and forming the pa- 

 rietes of the external dental cavity; it does not extend 

 into the pulp cavity. As Lecoq has indicated, " its thick- 

 ness is greater upon the anterior than upon the posterior 

 face of the tooth, and it also extends lower down upon the 

 former." It becomes quite thin towards the extremity of 

 the root. 



These facts, to which no importance has been attrib- 

 uted, nevertheless deserve to arrest our attention. It is 

 well known that there exist, upon the dental table, a certain 

 number of intermediary phases between the commencing 

 triangular form and the lateral flattening, or that which 

 Girard has called biangular. Nothing is more difficult, 

 then, than to determine whether a certain triangular form 

 is more recent than another which may differ but little 

 in shape. This is, nevertheless, a problem which an 

 attentive examination can solve, since we know that the 

 enamel will disappear earlier upon the surface of friction 

 behind than in front. It will suffice, then, to ascertain FIG. 285. Longitudinal 

 its relative thickness upon the periphery of the table ; or, antero-posterior section 



again, to prove its absence or its presence upon the pos- ho ^" n ^J^ ^{ 

 terior border of the tooth. The degree of wear of the sheath, A, prolonged in- 

 latter can thus, with practice, be easily determined. to the external dental 



An error rather frequently committed in France, and t cavit y- 

 which Messrs. Chauveau and Arloing have corrected, con- 



sists in believing that the layer of enamel which forms the wall of the external 

 dental cavity (central enamel) is prolonged in the form of a cone or enamel 

 horn well beyond the bottom of the external cavity properly so called. We 

 have demonstrated 3 that the sections upon which such a disposition is observed 

 are not made exactly according to the axis of the tooth, but pass to one side 

 of the latter. There results thus a more or less oblique section of the parietes 

 of this cone, which may deceive a superficial observer. Fig. 285, A, repre- 

 sents precisely such a section, and shows that similar ones can be obtained at 



Goubaux et Barrier, loc. cit. 



8 James Beart Simonds, The Age of the Ox, Sheep, and Pig, London, 1854, p. 34. 



8 Goubaux et Barrier, loc. cit. 



